I. Field of the Invention
The present invention relates to pneumatic tube conveyor systems and, in particular, to a unique means for converting a free dispatch pneumatic tube conveyor system into a controlled dispatch system.
II. Description of the Prior Art
In the most elementary tube conveyor systems a carrier is conveyed pneumatically directly from a dispatch terminal to a discharge terminal through one conveyor tube and is returned through another, the two tubes comprising a continuous air circuit. Since such a system is cumbersome and generally wasteful of material, conveyor systems have evolved from the simple point-to-point conveying system to the fully automated, computer-controlled systems that are commercially available today. With the advent of the ring dial carriers and the magnetic dial carriers, a greater potential of automation has also been realized. The simple point-to-point tube lines have been replaced by pairs of tube lines, each pair having the capacity to serve up to ten stations. The routing and switching of the carriers is accomplished electronically by reading the designation address selected on the body of the carrier. All sending inlets of the system are tied to one common tube line, while the receiving outlets are tied to another tube line. The two tube lines constitute the pair previously mentioned. To dispatch a carrier, it is necessary for an operator to open the sending inlet door and insert the carrier directly into the tube line. This method, while extremely simple, has serious disadvantages insofar that the operators have a tendency to insert several carriers, one after the other, into the tube line and, thus, overload the same. It is also known that the operators would insert carriers backwards into the system which made it impossible for proper routing, as such proper routing cannot be accomplished when the carrier is inserted in a rearward manner. Such rearward insertion of the carrier into the tube can also damage the carrier and the system. It is also known that operators have inserted foreign materials, such as paper, pencils, bottles and the like, into the system, all of which contribute to malfunctions and shutdowns in the system.
In certain situations operators are required to hold the sending inlet door open for a certain time after inserting the carrier. This can be a very difficult requirement to meet, as many operators will normally insert the carrier within the tube and immediately close the door. If a sufficient amount of time does not pass after the door has been held open, the carrier will stall in the tube line and will have to be retrieved. If, on the other hand, the door is held open for too long a period, the sending tube line can become disabled. Many of these problems have been recognized by pneumatic tube manufacturers; and to compensate, the manufacturers have introduced the so-called "Controlled Inlet Type" of system, which is commonly referred to as "Controlled Dispatch." In the controlled dispatch system the operator does not have direct access to the sending tube line, but instead there is a motorized valve called a slide gate which functions as a barrier to prevent the carrier from being directly inserted within the tube lines. Carriers cannot be dispatched backwards, nor can foreign material be inserted into the system. The carriers that are properly posiioned in the controlled dispatch mechanisms are dispatched in an orderly sequence as determined by a control center. Unfortunately, solutions to the prior art problems and the improvements brought by the controlled dispatch system benefit only users who have bought such systems during the initial construction of the building that utilizes the controlled dispatch conveyor system. To convert the free dispatch system to a controlled dispatch system requires extensive and costly rework of the existing equipment and facilities. Old stations must be replaced with new stations, while tube lines must be rerouted, necessitating the removal of walls, ceilings and the like and their reconstruction. Since the controlled dispatch station is considerably longer than the free dispatch station, there are numerous problems with masonry that may not always be solved to the owner's satisfaction. It would therefore be desirable to provide a simple and inexpensive means for converting a free dispatch system to a controlled dispatch system. The relevant prior art patents known to applicant are U.S. Pat. Nos. 3,767,138; 3,998,405; 3,237,883; and 3,404,921; and Great Britain Pat. No. 1,333,596. These patents were cited in the aforementioned United States patent application Ser. No. 775,257.